The present invention relates to a needle-card adjusting device for planarizing needle sets on a needle card (also referred to as a probe card) in relation to a wafer with which contact is to be made, in which the needle card is connected to a circuit board used as a contact interface to a test head.
Published, Non-Prosecuted German Patent Application DE 25 44 735 A1 discloses a test-head carrier with the aid of which the distance between individual test heads which carry test tips can be adjusted. This is intended to achieve adaptation of the test heads to the various shrinkages of ceramic substrates.
Furthermore, U.S. Pat. No. 5,861,859 describes an automatic planarizing system for test cards, in which a test card is adjusted with respect to a wafer surface. In which, first, three tips on the test card, of which two can be varied vertically, are aligned with the wafer surface.
As is known, needle sets on needle cards produce the electrical connection between individual contact pads or points on chips and a test head, in order in this way to check the serviceability of the chips on the wafer. In this wafer, the planarizing of the needle sets on the needle card in relation to the wafer with which contact is to be made, or the chips contained in the latter, becomes more and more complicated with the increasing number of the chips with which contact is to be made simultaneously. This is because the needle sets must be adjusted precisely to the contact pads respectively assigned to them on the chips, down to the order of magnitude of xc2xc xcexcm.
At the same time, it is to be noted that, in addition to the static adjustment of the needle card relative to the chips, dynamic components also have to be taken into account, these being caused, for example, by thermal expansion of the needle card during heating up or cooling down via a wafer holding device, also referred to as a xe2x80x9cchuckxe2x80x9d. Other dynamic components can be traced back to aging effects of the needle cards, on which the needle sets are mostly adhesively bonded. However, the dynamic components can also have very short time constants, such as in the case of vibrations.
In the case of needle sets that are adhesively bonded to the needle card, these have previously not been adjusted or have been adjusted only by a subsequent bending of each individual needle, which results in a considerable expenditure in time and money with the required accuracy down to xc2xc xcexcm. If the needle sets are fitted to so-called space transformers, then they can be adjusted with the aid of simple screws, with which, however, the indicated accuracy can barely be achieved.
It is accordingly an object of the invention to provide a needle-card adjusting device for planarizing needle sets on a needle card which overcomes the above-mentioned disadvantages of the prior art devices of this general type, with which the needle sets on the needle card can readily be planarized in relation to a wafer with which contact is to be made.
With the foregoing and other objects in view there is provided, in accordance with the invention, a combination of a needle card assembly having a needle-card with a plurality of needle sets, a test head, and a circuit board functioning as a contact interface to the test head, with a needle-card adjusting device for planarizing the needle sets on the needle card in relation to a wafer with which contact is to be made. The needle-card adjusting device includes a separate, dynamically operating adjusting unit connecting the needle card to the circuit board.
In the case of the needle-card adjusting device of the type mentioned at the beginning, according to the invention the object is achieved by the needle card being connected to the circuit board via a separate, dynamically operating adjusting unit. The adjusting unit is preferably constructed from at least one piezoelectric element. However, it can also contain a multiplicity of piezoelectric elements, which act on the needle card in the edge region thereof.
With the needle-card adjusting device according to the invention, the planarity of the needle card can readily be produced on site by dynamic adjustment. Therefore maladjustments of the needle card, which has been brought about for example by thermal expansion of the needle card or by brief vibration, can readily be corrected. Because of the dynamic adjustability of the needle card, the parallelism between the needle card and the wafer can be corrected when contact is made via the wafer edge.
Since, using the separate, dynamically operating adjusting unit, via which the needle card is connected to the circuit board, even dynamic effects can readily be corrected, any requirement for additional adjusting devices is dispensed with. In addition, the adjustment can be performed with the aid of a contact test loop, that is to say a program for the verification of the contact between each needle and an associated pad.
The adjusting unit can act in directions that are essentially perpendicular to the plane covered by the needle-card surface and/or in directions that are essentially in this plane.
As a result of constructing the adjusting unit from piezoelectric elements, in particular, its adjustability can be implemented with high precision.
In accordance with an added feature of the invention, there is provided a sense line, an active line, and a control unit connected to the dynamically operating adjusting unit through the sense line and the active line for controlling the dynamically operating adjusting unit.
In accordance with a concomitant feature of the invention, there is provided a stiffening device disposed between the needle card and the dynamically operating adjusting unit.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a needle-card adjusting device for planarizing needle sets on a needle card, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.